Metallic foams are metals that have porosity, and actually resemble foam or sponges. One particular metallic foam is called Trabecular metal, and is used as a material for bone implants. A foam material is useful in the body because the surrounding bone will grow into the cellular structure and the foam insert will generate a very strong bond with the natural bone. Trabecular metal is made of pure Tantalum metal. The problem with the material is that it cannot be cut using traditional machining methods. If the material is cut using traditional methods of machining, the cut surface smears. This is a problem because it reduces the porosity of the material surface and will therefore affect the functionality (inhibit bone in growth). Hence, manufacturers use methods such as electrical discharge machining (EDM), a spark erosion process that does not mechanically impinge on the material surface. There are significant limitations of using EDM, mainly due to the geometry that can be created easily. In one method, an EDM electrode is a shaped tool that can only be used for a particular custom shape. Another method is to use wire EDM, but it has limited ability to create geometry, in particular concave surfaces, since the wire must be able to span the surface.
If machining can be used, then custom shapes can be created, simply based on the tool motion and cutting paths. A great advantage of this is that custom bone implants can be created based on a computed tomography (CT) scan, MRI scans, or other x-rays of the patient. As such, a bone implant could be created for each patient individually.
Therefore, what is needed is a process of cutting metallic foams that eliminates the problem of smeared surfaces and allows machining to be used.